Continuous casting of metals



1956 H. WIELAND 2,772,459

CONTINUOUS CASTING "0F METALS Filed July 10, 1951 IN VENTOR' Y HAM/5"W/EL 4M9 A TTOEN Y5 United States Patent CUNTINUOU CASTING OF METALSHans Wieland, Ulm (Danube), Germany, assignor to Wieland Werke A. G.,Ulm (Danube), Germany, a corporation of Germany Application July10,1951, Serial No. 235,987

Claims priority, application Switzerland July 21, 1950 1 Claim. (Cl.22-2001) This invention relates to the continuous casting of metals. Inparticular, the invention is directed to the continuous casting ofmetals in an unlubricated mold.

In the ordinary casting of metals in a chilled mold, it is necessary touse a lubricant, usually containing carbon, on the casting surface ofthe mold in order to prevent sticking of the metal being cast.Otherwise, the mold becomes unserviceable, and the ingot is cast withsurface roughness, overlaps, and the like. However, the use of alubricant is but the lesser of two evils, for the lubricant may reactunfavorably with some metals and cause defects extending into the ingot,and incomplete combustion of the lubricant during casting will producesurface defects regardless of the metal being cast. Consequently, metalssuch as tough pitch copper, which are particularly sensitive to carboncontaining lubricants at fusion temperature a cannot be cast by acontinuous casting process, although, by contrast, a copper deoxidisedwith phosphorous can so be cast.

Non-metallic molds have been tried for continuous casting, including theuse of a non-metallic lining in a metal mold. Ordinary graphite has beentried as a lining, but as far as is known, has not heretofore beensuccessful due to rapid erosion and burning out. To avoid thesedifficulties, a special material has been used both as a mold by itself,and as a lining for a metallic mold. This material comprises chemicallyprecipitated graphite with colloidal carbon as a binding agent undervery high pressure, the porosity being at least and the grain size notgreater than microns. In the first case only small molds can be used andalthough satisfactory ingots are cast, the output is only about atwentieth of that obtainable with metal chill molds. The small output ofthe nonmetallic mold, together with certain apparatus difliculties,makes this mold unsatisfactory for production in quantity, even though agood ingot surface structure is obtained. In particular, neither anon-metallic mold nor a lined mold has been able to successfully castthe large quantities daily needed of tough pitch copper, even though nosupplernentary lubricant was needed.

The object of this invention is to produce a process for thelubricant-free continuous casting of metals, including the non-ferrousmetals and alloys, precious metals and alloys, iron, steel, and otherferrous metals and their alloys.

In general, these objects are achieved by constructing a metal mold withan ordinary graphite lining and a water cooling jacket of sufiicientcapacity to make the process possible. The molten metal poured into themold is solidified by contact with the chilled graphite lining at a rateto form a surface crust which will not be broken by the liquid moltenmetal core of the ingot as the ingot leaves the mold, and thenindirectly cooling the ingot to elfect the major heat extraction tosolidify the ingot interior.

The means by which the objects of the invention are obtained aredescribed morefully in the accompanying drawings, in which:

Figure l is a cross-sectional view through the lubricant free continuouscasting mold; and

2,772,459 Patented Dec. 4, 1956 Figure 2 is a plan view of the mold.

The mold is formed of an inner cylindrical member 1 telescoped within anouter member 2. inwardly turned flanges 2a and 212 at the ends of member2 serve to close the ends to form a water jacket between the inner andouter members. The lower end of inner member 1 is beveled and spacedfrom the beveled inner edge of flange 2b by means of set screws 3, whichare also used to adjust the height of the inner member 1 and fix thesize of the annular cooling fluid discharge opening 4. This opening hasless cross-sectional area than the inlet pipe 5 to insure the coolingjacket being kept full of fluid.

An ordinary graphite liner 7 is inserted in member 1, the liner restingon a collar 8 adjacent the lower edge of member 1.

According to the process of this invention, cooling fluid entering thecooling jacket produces a strong cooling action through liner 7 on themetal poured. into the mold, and the cooling medium discharged throughopening 4, causes an intensive cooling of the partially solidified ingotleaving the mold. Because of the strong cooling of liner 7, an ordinarygraphite liner can be used and kept at a temperature at which it is notattacked by the molten metal in the short period of time before themetal solidifies. Graphite exposed to air at a temperature of above 600C. will burn. By the process of this invention the graphite temperatureis kept below 600 C., and no oxidation is observed where the top surfaceof the molten metal touches liner 7. However, if higher castingtemperatures are encountered, a reducing atmosphere can be created bywell known means over thesurface of the molten metal.

As the molten metal fills the mold it is solidified against liner 7 intoa crust thick enough to keep the liquid interior from breaking throughas the ingot leaves the lower edge of member 1. The partially solidifiedingot is Withdrawn from the mold at a speed which permits solidificationof this crust. The thickness of this crust will vary within limits independence upon the metal cast, the cross-sectional area of the ingot,the intensity of the cooling both within and outside the mold, etc. Thecrust begins to form slightly below the upper surface of the moltenmetal in the mold and increases in thickness as the distance from theupper surface increases. It has been discovered that this crust isformed substantially as fast as a crust would be formed in an unlinedmold, and a comparable speed of casting achieved. As the graphite lining7 is self lubricating, the ingot being formed can slide downwardly andemerge from the mold without surface damage.

A practical operation of the process is given in the following example:

The slotted chill mold had a structural height of 200 mm. The graphitelining of the inner mold wall was 3 mm. thick. By the term graphitewithin the scope of the invention is to be understood all graphites ormaterials containing graphite which, like graphite-coated carbon, arenot moistened by molten materials and have been well tested in ironworksand metalworks for similar purposes. The internal diameter of the chillmold and the lining was 172 mm. The molten material for casting wassupplied to the mold from the forehearth of a furnace by means of anozzle pipe with an outlet diameter of 5.5 mm., said pipe beingresistance heated in known manner. The casting output was 2 tons perhour, both with tough pitch copper and with copper deoxidised withphosphorous. The surface of the casting was completely smooth and,.inparticular, free from annular folds and overlaps. The depth of the sumpin the centre of the ingot was 200 mm. The sump thus extended below thebottom edge of the mold, since the surface of the moldten metal in themold was about 50 mm. below the upper edge of the mold.. However, thesump may extend only up to the metal col lar 8, or the block, solidifiedover the entire cross-section,

, ,anvnnso may even extend into the non-metallic lining, when thecasting material undergoes a sudden direct cooling without heat stressesoccurring of such a height in the continuously cast block that they haveto be liberated in heat fissures. The solidification at the margincommenced about 1 cm. below the surface of the metal in a very thinmarginal layer becoming thicker in a downward direction. In the presentcase, a water trap was placed below the mold around the ingot, and nowater flowed through said trap ecausc the casting was so smooth that acomplete sealing against the outlet of water was produced. Thisadvantage was achieved with rubber rings.

By means of the process of the invention, primarily there is achieved'anessentially higher crude output of continuously cast products from metalchill molds with non-metallic linings, as compared with the formerlyknown outputs, the yield, surprisingly, corresponding to that which itis normally possible to obtain with undivided cooled metal chill molds,depending upon the nature of the material actually used, the compositionof the alloy, the cross section of the casting, the intensity of thedirect and indirect cooling, the length of the chill mold, etc. Inaddition, it is found that in accordance with the invention,continuously cast articles having a smooth surface are obtained whichare free from annular folds and overlaps, so that the solid or hollowcastings which are obtained can be supplied, without sWarf-removingtreatment, for further swarfless working, when they are not to bedirectly employed in the condition in which they are cast. As a resultof this particular condition which arises from the use of the invention,it is further found that the comparable pure output is even greater thanthat obtained by using the known undivided metal chill molds, becausewith the latter, the castings generally have to be subjccted to aswarf-removing treatment before undergoing the further swarfiesstreatment in order to eliminate surface defects on the cast products,such as rough surfaces, overlaps, etc. Only in special cases is theswarf-removing not necessary.

I The use of the lining 7 also increases the life and durability of thecasting mold, particularly in rough casting work.

It has hitherto been believed that in the continuous casting of metallicmaterials with the use of non-metallic casting molds, it was at leastnecessary to dissipate the whole of the fusion heat of the castingthrough the nonmetallic wall of the mold in order to achieve anappropri' ate angular position of the crystals in the solidifiedcasting,- such being "favourable for a subsequent swarfless finishingtreatment, and it was also attempted to employ this method of working inconnection with metal molds having a non-metallic inside wall in theupper part of the mold, but this did not work out in practice. With thelatter constructions, moreover, in another known process, not only wasthe aim to obtain no solidification at all in the region of thenon-metallic lining, but provision was even made by a heating actionthat in any case no marginal or surface crust solidification occurredwithin the meaning of the present invention, the result of which wasthat the marginal solidification which was subsequently establishedcould only commence in the metallic part of the combination mold.Because of the lack of a lubricant between the metal inside wall of themold and the solidified marginal crust of the casting, however, thecasting in the process remained adhering to the metal wall of the mold,so that it was not possible hitherto, with this proposal for metallicmaterials, to be continuously cast successfully. -However, if thispreviously known process was employed in accordance with anotherproposal in such manner that also no marginal solidification took placein the metallic bottom portion of the combination mold, then such aprocess again could not be exploited in practice, because the moltencasting core could not be caused to solidify so rapidly throughout thewhole cross-section that a softening of the already solidified marginalcrust 4. was excluded, which is however absolutely necessary for a safeprocess from the point of view of accidents.

Since with cooled metal chill molds, only a fraction of heat extractionfrom the molten casting material takes place indirectly through themetal inside wall of the mold, and the main heat extraction is usuallycarried out in known manner and with known means by the directlyfollowing abrupt cooling of the casting, which is at least solidified inits marginal crust, the heat extraction from the casting material inmolds having non-metallic internal walls must be even smaller with thearrangements already known. In these processes, the direct cooling ofthe casting has been abandoned in many cases, and it has frequently beenpreferred to employ the indirect cooling method. The consequence ofthis, however, is that the casting speed must be adapted to theessentially slower solidification speed at the expense of the former,especially when the casting mold is combined with the furnace, wherebythere is produced a lower output of continuously cast products ascompared with a process using cooled metal chill molds. metal chillmolds with a nonmetallic lining, so long as in this case thesolidification of the casting throughout the entire cross-section withinthe region of the non-metallic lining is sought after.

The process of the instant invention canbe employed for the continuouscasting of all metallic materials, whether they be light metals,non-ferrous heavy metals and their alloys, iron, steel, ferrous metalsand their alloys, and the like. However, it is particularly advantageousthat it is now possible for tough pitch copper to be continuously castby the process of the invention. As is known, with this material, uponthe solidification at the grain limits, the known copper-copper oxideeutectic alloy is separated out. and this can easily be reduced justbeneath the melting point of the copper by substances having a reducingaction, such as, for example, hydrogen, carbon, carbon monoxide, etc.This reaction results in the damage to the copper known under the nameof hydrogen defect, because due to the removal of the oxygen by thesereducing agents, the cohesion between the crystal grains is loosened, sothat with the swarfiess shaping in the cold or hot state, fissures areunavoidably produced which make unserviceable the semi-finished articlesproduced from the cast block.

The process according to the invention can also be used with advantagewith alloys which tend to reverse ingot liquation. With the known cooledmetal molds, the reverse ingot liquation with alloys which readilyliquate is promoted by various conditions. In contrast hereto, thereverse liquation in the process according to the invention is checkedon the one hand due to the lower heat conductivity of the graphite and011 the other hand due to the increased resistance to passage of heatbetween the graphite and copper wall.

The resistance capacity of the combination mold employed according tothe invention as regards mechanical stresses is in no way inferior tothat of a comparable cooled metal chil'l mold.

It is also important that with the process of the invention, thedirection of solidification is guided into the direction of the axis ofthe casting.

Having now described the means by Which the objects of the invention areobtained, I claim:

The process for the continuous casting of oxygen hearing metals in ametal mold having an open top and open bottom, formed by an outer metaljacket of substantial structural strength supporting and reinforcing arelatively thin graphite liner having a thickness such that the innersurface thereof is coolable below a liner reactive temperature of about600 C. during casting, said mold being unconnected with the containerholding the source of metal so that the molten metal in themold can haveits own free surface, said method comprising pour- The same would applyfor knowning molten metal into the open top, cooling said jacket andwithdrawing the congealed metal from the open bottom, the fit of theliner in the jacket and the thickness of the liner being such that themold extracts heat from the congealing metal through the linersubstantially as intensively as an all-metal lubricated mold wouldextract heat, said 1 tiring. cooling and withdrawing being at such ratethat a free surface of molten metal is maintained in said mold, and theupper edge of the congealing crater shell is maintained in closeproximity to said free surface, and the crater shell is of considerabledepth, but of such thickness as not to break through at the lower edgeof the mold.

References Cited in the file of this patent UNITED STATES PATENTS253,176 Billings Feb, 7, 1882 2,136,394 2, i-i5,4 l 6 2,225,3732,242,350 2,264,288 2,284,703 2,301,027 2,363,695 2,376,518 2,517,9312,530,854 2,590,311

Poland et al. Nov. 15, Crainpton Jan. 31, Goss Dec. 17, Eldred 2 May 20,Betterton et al. Dec. 2, Welblund et at June 2, Ennor Nov. 3, iuppik -2Nov. 28, Spence May 22, Rossi Aug. 8, Brennan Nov. 21, Harter et a].lviar. 25,

FOREIGN PATENTS Great Britain Apr. 26, France May 10,

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